User:Amal Binsalman/sandbox

= Petite Mutation =

Introduction:
A mutation that produces small (petite > petite) anaerobic-like colonies had shown first in Yeast Saccharomyces cerevisiae and described by Boris Ephrussi and                                                                     his co-workers in(1949a) in Gif-sur- Yvette, France. The cells of Petite colonies were smaller than those of wild-type colonies, but the term “petite” refers to the colony,                                                             not cell size.

Causes:
The petite caused by deficiency in cytochromes (a, a3 + b) and a poverty of respiratory enzymes which engage in respiration in mitochondria. Due to the error in                                                                            the respiratory chain pathway,'petite' yeast is incapable of growing on media containing only non-fermentable carbon sources (such as glycerol or ethanol) and forming                                                          small colonies when grown in the presence of fermentable carbon sources (such as glucose). The absence or the mutation in mitochondrial DNA (termed "cytoplasmic Petites")                                                  can cause the Petite phenotype. Also, it can be produced by mutations in nuclear-encoded genes involved in oxidative phosphorylation.

Experiment
Petite mutants can be generated in the laboratory by using high-efficiency treatments which are acriflavine, ethidium bromide, and other treatments. Their mechanism is to break                                           down and eventual loss of mitochondrial DNA: if the treatment time increases, the amount of mitochondrial DNA will decrease. After prolonged treatment, Petites containing no                                                detectable mitochondrial DNA were obtained. It is a useful approach to illustrate the function of mitochondrial DNA in yeast growth.

Petite mutation inheritance
The inheritance pattern of genes existing in the cell organelles such as mitochondria which named cytoplasmic inheritance differs from nuclear genes pattern.

Segregational Petites (pet – ):
Mutants are created by nuclear mutations and exhibit Mendelian 1:1 segregation.

Neutral Petites (rho – N):
Neutral petite when crossed to wild-type, all offspring are wild-type. It has inherited mitochondrial DNA from wild-type parent, which is replicated in the offspring.

Suppressive Petites (rho – S):
Crosses between petite and wild-type, all offspring are Petite, showing &amp;quot;dominant&amp;quot; behavior to suppress wild-type mitochondrial function.

Most petite mutants are a suppressive type, and they differ from natural Petite by affecting the wild-type, although both are a mutation in mitochondrial DNA. Mitochondrial genome of yeast will be the first eukaryotic genome to be understood in terms of both structure and function and this should smooth the way to                                                                           understand the evolution of organelle genomes and its relationship with nuclear genomes. It is evident that Ephrussi’s work not only opened the field                                                                                                                                                                                       of extrachromosomal genetics, but also provide a fantastic incentive for the investigations which followed up to this day.